Cardiovascular responses elicited by intrathecal kinins in the conscious rat

Bradykinin Receptors Play a Critical Role in the Chronic Post-ischaemia Pain Model

Complex regional pain syndrome type-I (CRPS-I) is a chronic painful condition resulting from trauma. Bradykinin (BK) is an important inflammatory mediator required in acute and chronic pain response. The objective of this study was to evaluate the association between BK receptors (B₁ and B₂) and chronic post-ischaemia pain (CPIP) development in mice, a widely accepted CRPS-I model. We assessed mechanical and cold allodynia, and paw oedema in male and female Swiss mice exposed to the CPIP model. Upon induction, the animals were treated with BKR antagonists (HOE-140 and DALBK); BKR agonists (Tyr-BK and DABK); antisense oligonucleotides targeting B₁ and B₂ and captopril by different routes in the model (7, 14 and 21 days post-induction). Here, we demonstrated that treatment with BKR antagonists, by intraperitoneal (i.p.), intraplantar (i.pl.), and intrathecal (i.t.) routes, mitigated CPIP-induced mechanical allodynia and oedematogenic response, but not cold allodynia. On the other hand, i.pl. administration of BKR agonists exacerbated pain response. Moreover, a single treatment with captopril significantly reversed the anti-allodynic effect of BKR antagonists. In turn, the inhibition of BKRs gene expression in the spinal cord inhibited the nociceptive behaviour in the 14th post-induction. The results of the present study suggest the participation of BKRs in the development and maintenance of chronic pain associated with the CPIP model, possibly linking them to CRPS-I pathogenesis.

Upregulation of tachykinin NK-1 and NK-3 receptor binding sites in the spinal cord of spontaneously hypertensive rat: impact on the autonomic control of blood pressure

1 Effects of intrathecally (i.t.) injected tachykinin NK-1 and -3 receptor agonists and antagonists were measured on mean arterial blood pressure (MAP) and heart rate (HR) in awake unrestrained spontaneously hypertensive rats (SHR,15-week-old) and age-matched Wistar Kyoto rats (WKY). Quantitative in vitro autoradiography was also performed on the lower thoracic spinal cord of both strains and Wistar rats using specific radioligands for NK-1 receptor ([(125)I]HPP[Arg(3),Sar(9),Met(O(2))(11)]SP (3-11)) and NK-3 receptor ([(125)I]HPP-Asp-Asp-Phe-N-MePhe-Gly-Leu-Met-NH(2)). 2 The NK-1 agonist [Sar(9),Met(O(2))(11)]SP (650 and 6500 pmol) decreased MAP and increased HR in WKY. The fall in MAP was blunted in SHR and substituted by increases in MAP (65-6500 pmol) and more sustained tachycardia. The NK-3 agonist senktide (6.5-65 pmol) evoked marked increases in MAP and HR (SHR>>>WKY), yet this response was rapidly desensitized. Cardiovascular effects of [Sar(9),Met(O(2))(11)]SP (650 pmol) and senktide (6.5 pmol) were selectively blocked by the prior i.t. injection of LY303870 (NK-1 antagonist, 65 nmol) and SB235375 (NK-3 antagonist, 6.5 nmol), respectively. Antagonists had no direct effect on MAP and HR in both strains. 3 Densities of NK-1 and -3 receptor binding sites were significantly increased in all laminae of the spinal cord in SHR when compared to control WKY and Wistar rats. The dissociation constant was however not affected in SHR for both NK-1 (K(d)=2.5 nM) and NK-3 (K(d)=5 nM) receptors. 4 Data highlight an upregulation of NK-1 and -3 receptor binding sites in the thoracic spinal cord of SHR that may contribute to the hypersensitivity of the pressor response to agonists and to the greater sympathetic activity seen in this model of arterial hypertension.

Effects of alpha-lipoic acid on kinin B1 and B2 receptor binding sites in the spinal cord of chronically angiotensin-treated rats

A quantitative autoradiographic study was performed to determine whether kinin receptors are altered in the rat spinal cord in an experimental model of arterial hypertension under antioxidant therapy with alpha-lipoic acid. Sprague-Dawley rats were fed for 4 weeks with a normal chow diet or with an alpha-lipoic acid supplemented diet (1000 mg/kg feed), and treated for the last 2 weeks with angiotensin II (AT II) (200 ng/kg/min with an osmotic pump implanted s.c.). Control rats received either diet but not AT II. A 2-week administration of AT II increased significantly systolic blood pressure, the production of superoxide anion in the aorta and B1 receptor binding sites in the thoracic spinal dorsal horn. This treatment did not affect spinal B2 receptor binding sites, glycemia and insulinemia. The diet supplemented with alpha-lipoic acid reduced significantly the increase in systolic blood pressure, the production of aortic superoxide anion and prevented the increases of B1 receptor binding sites. Results show an association between the oxidative stress and the increases of B1 receptors and arterial blood pressure induced by AT II. Data also exclude the possibility that arterial hypertension is a primary mechanism leading to an increase of B2 receptor binding sites in the rat spinal cord.

Autoradiographic distribution and alterations of kinin B2 receptors in the brain and spinal cord of streptozotocin-diabetic rats

This study investigates whether bradykinin (BK) B(2) receptor binding sites are increased in the brain and thoracic spinal cord of streptozotocin (STZ)-diabetic rats at 2, 7, and 21 days posttreatment by in vitro autoradiography with the radioligand [(125)I]HPP-Hoe 140. In control and diabetic rats, specific binding sites for B(2) receptors were detected in the brain and in various laminae of the spinal cord, predominantly in superficial laminae (K(d)=34 pM). In diabetic rats, B(2) receptor densities were significantly increased in lamina l of the dorsal horn (+35% at 7 and 21 days), spinal trigeminal nucleus (+70% at 7 and 21 days) and nucleus tractus solitarius (+100% at 2 and 7 days). B(2) receptor analogues D-Arg[Hyp(3),Thi(5),D-Tic(7),Oic(8)]-BK (Hoe 140), 3-(4 hydroxyphenyl)propionyl-Hoe 140 (HPP-Hoe 140), LF16-0687 mesylate ((2-Pyrrolidinecarboxamide, N-[3-[[4-aminoiminomethyl)benzoyl]amino]propyl]-1-[[2,4-dichoro-3-[[(2,4-dimethyl-8-quinolinyl)oxy]methyl]phenyl]sulfonyl]-(2S)-(9Cl)), and BK decreased binding of [(125)I]-HPP-Hoe 140 in the spinal dorsal horn, with K(i) values of 0.5, 1.5, 3.2, and 3.7 nM, respectively. These values were not significantly different in diabetic rats at 7 days (0.5 (Hoe 140), 0.7 (HPP-Hoe 140), 1.2 (BK), and 1.7 (LF16-0687) nM). While des-Arg(10)-Hoe 140 was three orders of magnitude less potent than Hoe 140, B(1) receptor agonist (des-Arg(9)-BK) and antagonist (AcLys[D-betaNal(7),Ile(8)]des-Arg(9)-BK, R-715) did not affect [(125)I]-HPP-Hoe 140 binding at 1 microM concentration. Data suggest a very discrete and temporal increase of B(2) receptor density (without affinity changes) in the spinal cord and hindbrain of STZ-diabetic rats. This contrasts with the early induction and over-expression of B(1) receptors reported in the brain and spinal cord of STZ-diabetic rats.

Chronic effects of angiotensin-converting enzyme inhibition on kinin receptor binding sites in the rat spinal cord

With the use of in vitro receptor autoradiography, this study aims at determining whether the higher level of kinin B(2) receptor density in the spinal cord of the spontaneously hypertensive rat (SHR) is secondary to arterial hypertension and whether chronic treatment with angiotensin I-converting enzyme inhibitors (ACEI) can regulate neuronal B(1) and B(2) receptors. SHR received, from the age of 4 wk, one of the two ACEI (lisinopril or zofenopril, 10 mg x kg(-1) x day(-1)) or for comparison, the selective AT(1) antagonist (losartan, 20 mg x kg(-1) x day(-1)) in their drinking water for a period of 4, 12, and 20 wk. Age-matched untreated SHR and Wistar-Kyoto rats (WKY) were used as controls. B(2) receptor binding sites in most laminae were higher in SHR than in WKY from the age of 8 to 24 wk. Whereas B(1) receptor binding sites were significantly present in young SHR and WKY, they were barely detectable in adult rats. ACEI (16 and 24 wk) and AT(1) antagonist (24 wk) enhanced the number of B(2) without changing B(1) receptor binding sites. However, at 8 wk the three treatments significantly increased B(1) and decreased B(2) receptors in lamina I. It is concluded that 1) the higher density of B(2) receptors in the spinal cord of SHR is not due to hypertension, 2) kinin receptors are regulated differently by ACEI in neuronal and vascular tissues, and 3) aging may have a profound impact on levels of B(1) and B(2) receptors in the rat spinal cord.

Pharmacologic and autoradiographic evidence for an up-regulation of kinin B(2) receptors in the spinal cord of spontaneously hypertensive rats

1. The effects of intrathecally (i.t.) injected kinin B(1) and B(2) receptor agonists and antagonists were measured on mean arterial pressure (MAP) and heart rate (HR) of conscious unrestrained spontaneously hypertensive rats (SHR of 16 weeks old) and age-matched normotensive Wistar Kyoto (WKY). Quantitative in vitro autoradiographic studies were also performed on the thoracic spinal cord of both strains with specific radioligands for B(2) receptors, [(125)I]-HPP-Hoe 140, and B(1) receptors, [(125)I]-HPP-[des-Arg(10)]-Hoe140. 2. Bradykinin (BK) (0.81 - 810 pmol) increased MAP dose-dependently with increases or decreases of HR. The pressor response to BK was significantly greater in SHR. The cardiovascular response to 8.1 pmol BK was reversibly blocked by 81 pmol Hoe 140 (B(2) antagonist) but not by 81 - 810 pmol [des-Arg(10)]-Hoe 140 (B(1) antagonist) in both strains. 3. The B(1) receptor agonist, des-Arg(9)-BK (8100 pmol) produced either no effects or increased MAP with variable effects on HR. These responses were similar in both strains and were reversibly blocked by 81 pmol Hoe 140. Inhibition with 8100 pmol [des-Arg(10)]-Hoe 140 was not specific to B(1) agonist-mediated responses. 4. [(125)I]-HPP-Hoe 140 specific binding sites were predominantly located to superficial laminae of the dorsal horn and were significantly higher in SHR. Low levels of [(125)I]-HPP-[des-Arg(10)]-HOE 140 specific binding sites were found in all laminae of both strains. 5. It is concluded that the hypersensitivity of the cardiovascular response to BK is due to an increased number of B(2) receptors in the spinal cord of SHR and that B(1) receptors are unlikely involved in spinal cardiovascular regulation in SHR.

Kinin receptors in pain and inflammation

Kinins are among the most potent autacoids involved in inflammatory, vascular and pain processes. These short-lived peptides, including bradykinin, kallidin and T-kinin, are generated during tissue injury and noxious stimulation. However, emerging evidence also suggests that kinins are stored in neuronal elements of the central nervous system (CNS) where they are thought to play a role as neuromediators in various cerebral functions, particularly in the control of nociceptive information. Kinins exert their biological effects through the activation of two transmembrane G-protein-coupled receptors, denoted bradykinin B(1) and B(2). Whereas the B(2) receptor is constitutive and activated by the parent molecules, the B(1) receptor is generally underexpressed in normal tissues and is activated by kinins deprived of the C-terminal Arg (des-Arg(9)-kinins). The induction and increased expression of B(1) receptor occur following tissue injury or after treatment with bacterial endotoxins or cytokines such as interleukin-1 beta and tumor necrosis factor-alpha. This review summarizes the most recent data from various animal models which convey support for a role of B(2) receptors in the acute phase of the inflammatory and pain response, and for a role of B(1) receptors in the chronic phase of the response. The B(1) receptor may exert a strategic role in inflammatory diseases with an immune component (diabetes, asthma, rheumatoid arthritis and multiple sclerosis). New information is provided regarding the role of sensory mechanisms subserving spinal hyperalgesia and intrapleural neutrophil migration that occur upon B(1) receptor activation in streptozotocin-treated rats, a model of insulin-dependent diabetes mellitus in which the B(1) receptor seems to be rapidly overexpressed. Although it is widely accepted that the blockade of kinin receptors with specific antagonists could be of benefit in the treatment of somatic and visceral inflammation and pain, recent molecular and functional evidence suggests that the activation of B(1) receptors with an agonist may afford a novel therapeutic approach in the CNS inflammatory demyelinating disorder encountered in multiple sclerosis by reducing immune cell infiltration (T-lymphocytes) into the brain. Hence, the B(1) receptor may exert either a protective or detrimental effect depending on the inflammatory disease. This dual function of the B(1) receptor deserves to be investigated further.

Pharmacological characterization of the cardiovascular responses elicited by kinin B(1) and B(2) receptor agonists in the spinal cord of streptozotocin-diabetic rats

Kinin receptor agonists and antagonists at the B(1) and B(2) receptors were injected intrathecally (i.t., at T-9 spinal cord level) to conscious unrestrained rats and their effects on mean arterial pressure (MAP) and heart rate (HR) were compared in streptozotocin (STZ)-diabetic rats (65 mg kg(-1) STZ, i.p. 3 weeks earlier) and aged-matched control rats. The B(1) receptor agonist, des-Arg(9)-Bradykinin (BK) (3.2 - 32.5 nmol), evoked dose-dependent increases in MAP and tachycardia during the first 10 min post-injection in STZ-diabetic rats only. The cardiovascular response to 6.5 nmol des-Arg(9)-BK was reversibly blocked by the prior i.t. injection of antagonists for the B(1) receptor ([des-Arg(10)]-Hoe 140, 650 pmol or [Leu(8)]-des-Arg(9)-BK, 65 nmol) and B(2) receptor (Hoe 140, 81 pmol or FR173657, 81 pmol) or by indomethacin (5 mg kg(-1), i.a.). The i.t. injection of BK (8.1 - 810 pmol) induced dose-dependent increases in MAP which were accompanied either by tachycardiac (STZ-diabetic rats) or bradycardiac (control rats) responses. The pressor response to BK was significantly greater in STZ-diabetic rats. The cardiovascular response to 81 pmol BK was reversibly blocked by 81 pmol Hoe 140 or 81 pmol FR173657 but not by B(1) receptor antagonists nor by indomethacin in STZ-diabetic rats. The data suggest that the activation of kinin B(1) receptor in the spinal cord of STZ-diabetic rats leads to cardiovascular changes through a prostaglandin mediated mechanism. Thus, this study affords an accessible model for studying the expression, the pharmacology and physiopathology of the B(1) receptor in the central nervous system.

Centrally bradykinin B2-receptor-induced hypertensive and positive chronotropic effects are mediated via activation of the sympathetic nervous system

OBJECTIVE

The presence of bradykinin B2 receptors in the cardiovascular regulatory centres of the brain indicates that increase in mean arterial pressure (MAP) and heart rate after intracerebroventricular (i.c.v.) injections of bradykinin is mediated via stimulation of sympathetic nervous system.

METHODS

Adult Wistar- Kyoto (WKY) rats were instrumented chronically with an i.c.v. cannula, and the catheters were placed into the femoral artery and vein. Increasing doses of bradykinin (1 -300 pmol) were given i.c.v. and (i) MAP and heart rate, (ii) plasma dopamine, noradrenaline and adrenaline, and (iii) plasma arginine vasopressin (AVP) levels were determined. In addition, following blockade of peripheral alpha1 -adrenoceptors with prazosin (50 and 250 microg/kg i.v.) beta1-adrenoceptors with atenolol (10 mg/kg i.v.) or V1 -receptors with TMe-AVP (Manning compound) (10 microg/kg i.c.v. and 100 microg/kg i.v.) the effects of bradykinin (100 pmol i.c.v.) on MAP and heart rate were determined.

RESULTS

Bradykinin increased MAP and heart rate dose-dependently. The pressor effects of 100 pmol bradykinin i.c.v. were completely blocked by pretreatment with the specific B2 receptor antagonist Hoe 140 (3 pmol, i.c.v.). There was no change in plasma dopamine, noradrenaline, adrenaline or AVP levels after increasing doses of bradykinin. However, peripheral blockade of alpha1- and beta1-adrenoceptors reduced the bradykinin-induced increase in MAP and heart rate, whereas central and peripheral V1 receptor blockade did not alter the cardiovascular responses to i.c.v. bradykinin.

CONCLUSION

Our data suggest that the hypertensive and positive chronotropic effects induced by i.c.v. bradykinin are due to stimulation of sympathoneuronal rather than sympathoadrenal pathway in vivo.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Bradykinin receptors and their antagonists

Bradykinin and related kinins act on two receptor types, named B1 and B2. Initially identified in classical bioassays, these receptors have been cloned and characterized in binding assays performed on plasma membranes of cells expressing the native or the transfected human kinin B1 or B2 receptor types. The two classification criteria recommended by Schild, namely the order of potency of agonists and the actual affinity of antagonists have been found to be applicable for receptor classification based not on data only from bioassays but also from other approaches (binding assays, molecular biology techniques). The order of potency for agonists was found with naturally occurring peptides (the kinins, their desArg9-metabolites) and with selective agonists (e.g., [Hyp3]bradykinin, [Aib7]bradykinin): the findings obtained with agonists could be validated with various antagonists. Critical evaluation of the initial compounds, typified by D)-Arg-[Hyp3, D-Phe7]bradykinin, has indicated that they are short-acting, partial agonists, non-selective for the bradykinin B2 receptor because they can be metabolized to desArg9-fragments that act on the kinin B1 receptor. Use of such compounds has given rise to misunderstandings, especially with regard to new receptor types (e.g., type B3), the existence of which was not confirmed by molecular cloning. A second generation of antagonists, represented by D-Arg[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (HOE 140) has been found resistant to degradation, long-acting in vivo, selective and specific for the B2 receptor and potent in all species tested. HOE 140 has been used successfully in basic pharmacology, in animal physiopathologies involving kinins and their receptors and even in clinical studies. A third generation of non-peptide B2 receptor antagonists, whose prototype is FR 173657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-2-4-dichloro-3-[(2-methyl-8-quinolin yl)oxymethyl]phenyl]-N-methylamino carbonyl-methyl]acrylamide) is now emerging and may represent substantial progress since FR 173657 is a potent orally active, selective and specific antagonist of the human and other species B2 receptors. There is also progress regarding antagonists for the B1 receptor. The initial compounds, especially Lys-[Leu8]desArg9-bradykinin remain among of the most potent, specific and selective B1 antagonists which, however, show partial agonistic effects in some B1 receptor subtypes (e.g., the mouse). Progress has been made with AcLys-[D-betaNal7, Ile8]desArg9-bradykinin (R 715) and Lys-Lys-[Hyp3, Cpg5, D-Tic7,Cpg8]desArg9-bradykinin (B 9958) which are pure B1 antagonists in humans and rabbits; both peptides have shown resistance to degradation by peptidases and have little if any, residual agonistic activity on mouse and rat B1 receptors. No non-peptide antagonists are yet available for the B1 receptor.

Synthesis of kininogen and degradation of bradykinin by PC12 cells

1. In this study, the abilities of PC12 cells to synthesize and degrade kinins were investigated. Kinin formation was assessed as kinin and kininogen content of cells and supernatants in serum-free incubations by use of a bradykinin-specific radioimmunoassay. Expression of kininogen mRNA was demonstrated by reverse-transcriptase PCR. Kinin degradation pathways of intact PC12 cells were characterized by identification of the kinin fragments generated from tritiated bradykinin either in the absence or presence of the angiotensin I-converting enzyme inhibitor ramiprilat. 2. Kinin immunoreactivity in the supernatant of PC12 cell cultures accumulated in a time-dependent fashion during incubations in serum-free media. This effect was solely due to de novo synthesis and release of kininogen (35 pg bradykinin h-1 mg-1 protein) since it could be suppressed by cycloheximide. Continuous synthesis of kininogen was a specific property of PC12 cells, as it was not observed in cultured macro- or microvascular endothelial cells. PC12 cells contained only minor amounts of stored kininogen. The rate of kininogen synthesis was not affected by ramiprilat, bacterial lipopolysaccharide, nerve growth factor or dexamethasone, but was stimulated 1.4 fold when cells were pretreated for 1 day with 1 microM desoxycorticosterone. 3. By use of cDNA probes specific for kininogen subtype mRNAs, expression of low-molecular-weight kininogen and T-kininogen in PC12 cells was confirmed. Expression of high molecular weight kininogen mRNA was also shown, though only at the lowest limit of detection of the assay. 4. Degradation of tritiated bradykinin by PC12 cells occurred with a half-life of 48 min resulting in the main fragments [1-7]- and [1-5]-bradykinin. The degradation rate of bradykinin decreased to 15% in the presence of ramiprilat (250 nM). Apart from angiotensin I-converting enzyme direct cleavage of bradykinin to [1-7]- and [1-5]-bradykinin still occurred under this condition as a result of additional kininase activities. 5. Along with previous findings of B2-receptor-mediated catecholamine release, these results now confirm the hypothesis that a cellular kinin system is expressed in PC12 cells. The presence of such a system may reflect a role of kinins as local neuromodulatory mediators in the peripheral sympathetic system.

Localization of bradykinin-like immunoreactivity in the rat spinal cord: effects of capsaicin, melittin, dorsal rhizotomy and peripheral axotomy

A putative role for bradykinin has been proposed in the processing of sensory information at the level of the spinal cord. Autoradiographic studies have demonstrated the presence of B2 kinin receptor binding sites in superficial laminae of the dorsal horn and a down-regulation of those receptors in rat models of pain injury. In this study, classical immunocytochemistry and confocal microscopy immunofluorescence were used first to localize bradykinin-like immunoreactivity in all major spinal cord segments of naive rats; second, to assess bradykinin-like immunoreactivity changes that occur in animals subjected to various chemical treatments and surgical lesions. High densities of bradykinin-like immunoreactivity were observed in motoneuron of the ventral horn, deeper laminae and nucleus dorsalis of the dorsal horn. Higher magnification of ventral horn showed strong immunostaining of motoneuron perikaryas and their proximal processes. Two types of bradykinin-like immunoreactivity immunostained cellular bodies were observed in deeper laminae of the dorsal horn. These interneurons, morphologically corresponding to islets and antenna-type cells project dendrites to adjacent laminae. Furthermore, numerous strongly marked dendrites, transversally cut, suggest the presence of projection neurons to higher cervical centres. Following unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesion of the sciatic nerve, important increases of bradykinin-like immunoreactivity were found in laminae III and IV of the ipsilateral dorsal horn. In contrast, significant decreases of immunodeposits were observed in both cell bodies and numerous dendrites of motoneuron surrounding neuropil. Specific destructions of sensory afferent fibres with capsaicin or selective activation of kallikreins with melittin caused increases of bradykinin-like immunoreactivity in both the dorsal and ventral horns of the spinal cord. These results which demonstrate the cellular localization of bradykinin-like immunoreactivity in both dorsal and ventral horns of the rat spinal cord, further reveal the plasticity of this non-sensory peptidergic system following various chemical and surgical treatments. Hence, these anatomical findings along with earlier functional and receptor autoradiographic studies reinforce the putative role of bradykinin in sensory function.

Quantitative autoradiographic localization of [125I-Tyr8]bradykinin receptor binding sites in the rat spinal cord: effects of neonatal capsaicin, noradrenergic deafferentation, dorsal rhizotomy and peripheral axotomy

In vitro receptor autoradiography was used to localize, quantify and characterize [125I-Tyr8]bradykinin binding sites in all major spinal cord segments of normal rats and animals subjected to various chemical treatments and surgical lesions. [125I-Tyr8]bradykinin specific binding sites were predominantly located to superficial laminae of the rat dorsal horn, with the substantia gelatinosa showing the highest density of labelling (values ranging from 3.1 fmol/mg tissue in cervical to 4.5 fmol/mg tissue in lumbar segments). A moderate density (1.8-3.0 fmol/mg tissue) of specific binding was observed in lamina III, whereas in other areas, i.e. laminae I and IV-X, lower amounts of labelling were detected. Within the superficial laminae of the dorsal horn, [125I-Tyr8]bradykinin binding was largely distributed over the neurophil with some perikarya showing concentrations of labelling. In contrast, the ventral horn showed a rather homogeneous distribution of [125I-Tyr8]bradykinin binding over the neuropil, with silver grain alignments surrounding motoneuron perikaryas and proximal processes. Bradykinin, [Tyr8]bradykinin and B2 receptor antagonists (D-Arg[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (Hoe 140), D-Arg[Tyr3,D-Phe7,Leu8]bradykinin, D-Arg[Hyp3, Leu8]bradykinin, D-Arg[Hyp2, Thi5,8,-Phe7]bradykinin D-Arg[Hyp3, D-Phe7, Leu8]bradykinin, Tyr0, D-Arg[Hyp3, D-Phe7, Leu8]bradykinin inhibited [125I-Tyr8]-bradykinin binding with very high subnanomolar affinities, while the B1 receptor agonist (Tyr0,des-Arg10-kallidin) and antagonist ([Leu8]-des-Arg9-bradykinin) did not significantly affect [125I-Tyr8]bradykinin binding at up to micromolar concentrations. Two weeks after unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesions of the sciatic nerve, significant decreases ( +/- 50%) in [125I-Tyr8]bradykinin binding sites were found in ipsilateral laminae I-III of lumbar spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinins and kinin receptors in the nervous system

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

Cardiovascular effects of intrathecally administered endothelins and big endothelin-1 in conscious rats: receptor characterization and mechanism of action

In conscious rats, the intrathecal (i.t.) injection of endothelin-1 (ET-1; 65-650 pmol) and endothelin-3 (ET-3; 162-650 pmol) produced dose-dependent increases of mean arterial blood pressure (MAP) accompanied by either a tachycardia or a bradycardia. A number of animals died by a sudden respiratory arrest. ET-3 was less toxic and less potent than ET-1 on MAP and heart rate (HR) while BQ-3020, a selective ETB agonist, had no toxic effect and exhibited only a weak pressor effect on blood pressure. The prior i.t. injection of 65 nmol BQ-123, a selective ETA receptor antagonist, blocked both the cardiovascular and toxic effects of ET-1 but failed to modify the cardiovascular effect evoked by i.t. substance P (6.5 nmol) or to cause intrinsic cardiovascular and toxic effects. While the pressor response to ET-1 was significantly inhibited after i.v. injection of phentolamine, the bradycardia was blocked by pentolinium. The cardiovascular response to ET-1 was, however, unaffected in rats either sympathectomized with 6-hydroxydopamine or pretreated with capsaicin. Furthermore, big ET-1 (100 pmol) caused toxic effects and delayed cardiovascular changes which were prevented by the prior i.t. administration of either BQ-123 (65 nmol) or 100 nmol phosphoramidon, an endothelin-converting enzyme (ECE) inhibitor. These results suggest: (1) that the cardiovascular and toxic effects of i.t. endothelins are mediated by ETA receptors in the rat spinal cord; (2) that the pressor response and bradycardia are likely due to the activation of the sympatho-adrenal nervous system and to a vagal reflex mechanism, respectively; and (3) that a phosphoramidon-sensitive ECE converts big ET-1 to ET-1 in the rat spinal cord.

Cardiovascular effects of intrathecally administered bradykinin in the rat: characterization of receptors with antagonists

1. The effects of intrathecal (i.t.) pretreatment with selective B1 or B2 kinin receptor antagonists were studied on the cardiovascular response to i.t. injection of bradykinin (BK) in conscious freely moving rats. 2. BK (81 pmol) produced an increase in mean arterial pressure (MAP: 9-13 mmHg) and decrease in heart rate (HR: 20-30 beats min-1) that reached a maximum 2 min after injection. 3. The BK-induced cardiovascular responses were dose-dependently and reversibly reduced by four antagonists with the following rank order of potency: Tyr, D-Arg[Hyp3,D-Phe7,Leu8]-BK = D-Arg[Tyr3,D-Phe7,Leu8]-BK = D- Arg[Hyp3,D-Phe7,Leu8]-BK > D-Arg[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe 140). These compounds failed to alter the cardiovascular response to i.t. injection of 8.1 nmol of substance P. 4. Other compounds acting on the B2 receptor, namely D-Arg[Hyp3,Gly6,Leu8]-BK, D-Arg[Hyp3,D-Phe7]-BK, D-Arg[Hyp2,Thi5,8,D-Phe7]-BK and D-Arg[Hyp3,Gly6,D-Phe7,Leu8]-BK or on the B1 receptor, [Leu8]-desArg9-BK, did not influence the cardiovascular responses to BK at doses devoid of intrinsic activity on MAP and HR. 5. None of the kinin receptor antagonists caused motor impairment, respiratory arrest or persisting cardiovascular changes. 6. These results confirm that the cardiovascular effects induced by i.t. BK are mediated by the activation of a B2 receptor in the rat spinal cord. However, the rank order of potency of antagonists does not conform to the classical B2 functional site characterized in peripheral tissues.

Autoradiographic localization of [125I-Tyr8]-bradykinin receptor binding sites in the guinea pig spinal cord

The present study aimed to localize and characterize [125I-Tyr8]-BK binding sites in all major segments of the guinea pig spinal cord using in vitro quantitative receptor autoradiography. [125I-Tyr8]-BK specific binding sites were localized predominantly in superficial layers of the dorsal horn, with lamina II depicting the highest labelling. The density of specific binding in laminae I and III was moderate, whereas in other areas, i.e., laminae IV-X, lower amounts of labelling were noticed. The B2 receptor antagonists D-Arg[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe 140), D-Arg[Hyp3,D-Phe7,Leu8]-BK, Tyr0,D-Arg[Hyp3,D-Phe7,Leu8]-BK, D-Arg[Tyr3,D-Phe7,Leu8]-BK, D-Arg[Hyp2,Thi5,8,D-Phe7]-BK, D-Arg[Hyp3,Leu8]-BK and D-Arg[Hyp3,Gly6,Leu8]-BK as well as unlabelled [Tyr8]-BK inhibited [125I-Tyr8]-BK binding with respective Ki values of 0.04, 12.4, 23.4, 34.5, 43.5, 33.5, 23.0, and 0.6 nM while B1 related molecules (Tyr0,des-Arg10-kallidin and [Leu8]-des-Arg9-BK) did not significantly inhibit [125I-Tyr8]-BK binding up to micromolar concentrations. These results indicate that the specific [125I-Tyr8]-BK binding sites present in the guinea pig spinal cord belong to the B2 receptor subtype. The high density of B2 binding sites in the substantia gelatinosa provides an anatomical evidence in favour of a role for BK as a modulator of nociceptive information.

Inhibitory action of (+/-)CP-96,345 on the cardiovascular responses to intrathecal substance P and neuropeptide K in the conscious freely moving rat

(+/-)CP-96,345, a nonpeptide and highly selective NK-1 receptor antagonist, was tested acutely and chronically as an inhibitor of the cardiovascular responses induced by the intrathecal (i.t.) injection of substance P (SP) and neuropeptide K (NPK) in the conscious rat. When given at T-9 spinal cord level, NPK (0.65, 3.25 and 6.5 nmol) and SP (6.5, 16.25 and 32.5 nmol) produced increases in mean arterial pressure and heart rate. The cardiovascular responses to NPK were greater in intensity and duration than those produced by SP. The prior i.t. injection of (+/-)CP-96,345 (0.65 and 6.5 nmol, 15 min earlier) inhibited in a dose-dependent manner the pressor response and the tachycardia induced by 6.5 nmol SP while 65 nmol of the antagonist was required to reduce the effects of 3.25 nmol NPK. However, both the SP and NPK-induced cardiovascular changes were blocked 2 days after the i.t. injection of 6.5 nmol (+/-)CP-96,345. Five days after a single i.t. injection of 6.5 nmol (+/-)CP-96,345, the cardiovascular response to SP remained unaffected while that of NPK was partially attenuated. Moreover, (+/-)CP-96,345 was active as an antagonist when given i.v. at the dose of 0.13 mg/kg. Conversely, (+/-)CP-96,345 failed to block the cardiovascular effect caused by the i.t. injection of 81 pmol bradykinin and did not produce any changes on resting blood pressure and heart rate when given alone either i.t. or i.v.(ABSTRACT TRUNCATED AT 250 WORDS)